Abstract

Mountainous terrain creates variability in microclimate, including nocturnal cold air drainage and resultant temperature inversions. Driven by the elevational temperature gradient, vapor pressure deficit (VPD) also varies with elevation. Soil depth and moisture availability often increase from ridgetop to valley bottom. These variations complicate predictions of forest productivity and other biological responses. We analyzed spatiotemporal air temperature (T) and VPD variations in a forested, 27-km(2) catchment that varied from 1000 to 1650 m in elevation. Temperature inversions occurred on 76% of mornings in the growing season. The inversion had a clear upper boundary at midslope (similar to 1370 m a.s.l.). Vapor pressure was relatively constant across elevations, therefore VPD was mainly controlled by T in the watershed. We assessed the impact of microclimate and soil moisture on tree height, forest productivity, and carbon stable isotopes (delta C-13) using a physiological forest growth model (3-PG). Simulated productivity and tree height were tested against observations derived from lidar data. The effects on photosynthetic gas-exchange of dramatic elevational variations in T and VPD largely cancelled as higher temperature (increasing productivity) accompanies higher VPD (reducing productivity). Although it was not measured, the simulations suggested that realistic elevational variations in soil moisture predicted the observed decline in productivity with elevation. Therefore, in this watershed, the model parameterization should have emphasized soil moisture rather than precise descriptions of temperature inversions.

Keywords

Cold-air drainage; Soil moisture; Environmental lapse rate; Tree height; delta C-13; Forest growth

Published in

Agricultural and Forest Meteorology
2018, Volume: 259, pages: 211-221
Publisher: ELSEVIER SCIENCE BV

SLU Authors

• Marshall, John

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    
  • University of Idaho

Sustainable Development Goals

Take urgent action to combat climate change and its impacts


UKÄ Subject classification

Forest Science


Publication identifier

DOI: https://doi.org/10.1016/j.agrformet.2018.05.012

Permanent link to this page (URI)

https://res.slu.se/id/publ/95969